129 research outputs found
Understanding Current Signals Induced by Drifting Electrons
Consider an electron drifting in a gas toward a collection electrode. A
common misconception is that the electron produces a detectable signal only
upon arrival at the electrode. In fact, the situation is quite the opposite.
The electron induces a detectable current in the electrode as soon as it starts
moving through the gas. This induced current vanishes when the electron arrives
at the plate. To illustrate this phenomenon experimentally, we use a gas-filled
parallel plate ionization chamber and a collimated Am alpha source,
which produces a track of a fixed number of ionization electrons at a constant
distance from the collection electrode. We find that the detected signal from
the ionization chamber grows with the electron drift distance, as predicted by
the model of charge induction, and in conflict with the idea that electrons are
detectable upon arrival at the collection plate.Comment: 21 pages, 12 figure
The First Lunar Ranging Constraints on Gravity Sector SME Parameters
We present the first constraints on pure-gravity sector Standard-Model
Extension (SME) parameters using Lunar Laser Ranging (LLR). LLR measures the
round trip travel time of light between the Earth and the Moon. With 34+ years
of LLR data, we have constrained six independent linear combinations of SME
parameters at the level of to . There is no evidence for
Lorentz violation in the LLR dataset.Comment: 7 pages, presented at the Fourth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, August 200
Updates from the Dark Matter Time Projection Chamber Group (DMTPC)
The Dark Matter Time Projection Chamber (DMTPC) collaboration has developed a series of gas-based detectors with the goal of detecting the directional anisotropy of dark-matter-induced nuclear recoils. Here, we report on recent progress from the DMPTC group, focusing on the surface operation of the 4shooter detector
Gain Stabilization of a Submillimeter SIS Heterodyne Receiver
We have designed a system to stabilize the gain of a submillimeter heterodyne
receiver against thermal fluctuations of the mixing element. In the most
sensitive heterodyne receivers, the mixer is usually cooled to 4 K using a
closed-cycle cryocooler, which can introduce ~1% fluctuations in the physical
temperature of the receiver components. We compensate for the resulting mixer
conversion gain fluctuations by monitoring the physical temperature of the
mixer and adjusting the gain of the intermediate frequency (IF) amplifier that
immediately follows the mixer. This IF power stabilization scheme, developed
for use at the Submillimeter Array (SMA), a submillimeter interferometer
telescope on Mauna Kea in Hawaii, routinely achieves a receiver gain stability
of 1 part in 6,000 (rms to mean). This is an order of magnitude improvement
over the typical uncorrected stability of 1 part in a few hundred. Our gain
stabilization scheme is a useful addition to SIS heterodyne receivers that are
cooled using closed-cycle cryocoolers in which the 4 K temperature fluctuations
tend to be the leading cause of IF power fluctuations.Comment: 7 pages, 6 figures accepted to IEEE Transactions on Microwave Theory
and Technique
Dark Matter Time Projection Chamber: Recent R&D Results
The Dark Matter Time Projection Chamber collaboration recently reported a dark matter limit obtained with a 10 liter time projection chamber filled with CF4 gas. The 10 liter detector was capable of 2D tracking (perpendicular to the drift direction) and 2D fiducialization, and only used information from two CCD cameras when identifying tracks and rejecting backgrounds. Since that time, the collaboration has explored the potential benefits of photomultiplier tube and electronic charge readout to achieve 3D tracking, and particle identification for background rejection. The latest results of this effort is described here
Testing for Lorentz Violation: Constraints on Standard-Model-Extension Parameters via Lunar Laser Ranging
We present constraints on violations of Lorentz invariance based on archival lunar laser-ranging (LLR) data. LLR measures the Earth-Moon separation by timing the round-trip travel of light between the two bodies and is currently accurate to the equivalent of a few centimeters (parts in 1011 of the total distance). By analyzing this LLR data under the standard-model extension (SME) framework, we derived six observational constraints on dimensionless SME parameters that describe potential Lorentz violation. We found no evidence for Lorentz violation at the 10-6 to 10-11 level in these parameters. This work constitutes the first LLR constraints on SME parameters
Testing for Lorentz Violation: Constraints on Standard-Model-Extension Parameters via Lunar Laser Ranging
We present constraints on violations of Lorentz invariance based on archival lunar laser-ranging (LLR) data. LLR measures the Earth-Moon separation by timing the round-trip travel of light between the two bodies and is currently accurate to the equivalent of a few centimeters (parts in 1011 of the total distance). By analyzing this LLR data under the standard-model extension (SME) framework, we derived six observational constraints on dimensionless SME parameters that describe potential Lorentz violation. We found no evidence for Lorentz violation at the 10-6 to 10-11 level in these parameters. This work constitutes the first LLR constraints on SME parameters
APOLLO clock performance and normal point corrections
The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) has produced a large volume of high-quality lunar laser ranging (LLR) data since it began operating in 2006. For most of this period, APOLLO has relied on a GPS-disciplined, high-stability quartz oscillator as its frequency and time standard. The recent addition of a cesium clock as part of a timing calibration system initiated a comparison campaign between the two clocks. This has allowed correction of APOLLO range measurements--called normal points--during the overlap period, but also revealed a mechanism to correct for systematic range offsets due to clock errors in historical APOLLO data. Drift of the GPS clock on ~1000 s timescales contributed typically 2.5 mm of range error to APOLLO measurements, and we find that this may be reduced to ~1.6 mm on average. We present here a characterization of APOLLO clock errors, the method by which we correct historical data, and the resulting statistics
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